Earplug with improved audibility

Abstract

An earplug uses damping to render unimportant a Helmholtz resonance between the acoustic mass intrinsic to a sound channel thereof and the compliance of air in the earcanal unimportant, in combination with an external structure coupled to the sound channel to increase response characteristics at higher frequencies in a predictable and well controlled manner in order to provide a highly desireable uniform frequency response.

I claim: 
     
       1. A protective earplug with improved audibility, comprising: first passage means arranged for positioning with at least an inner end portion thereof in an earcanal to define a first sound passage extending from an inner end within the ear canal to an opposite outer end, a relative large acoustic resistance means arranged for cooperation with an intrinsic acoustic mass reactance of said first passage and an intrinsic acoustic compliance of the ear canal to provide a substantially non-resonant acoustic impedance, and second passage means defining a second sound passage having an inner end coupled to said outer end of said first passage and having an opposite sound-receiving outer end, said second passage being operative to increase response characteristics at frequencies in an audible spectrum above approximately 800 Hz. 
     
     
       2. An earplug as defined in claim 1, said second passage having a length of approximately one-fourth wavelength at a frequency at which the response of the ear is at a maximum. 
     
     
       3. An earplug as defined in claim 1, said outer end of said second passage forming a sound inlet for said earplug and being positioned in proximity to an entrance to the earcanal. 
     
     
       4. An earplug as defined in claim 3, said second passage having a reverse bend therein. 
     
     
       5. An earplug as defined in claim 3, said second passage having a spiral shape. 
     
     
       6. An earplug as defined in claim 1, said first passage means comprising a generally straight tube, and a compressible foam member surrounding said tube. 
     
     
       7. An earplug as defined in claim 6, said tube having an outside diameter which is a small fraction of an inside diameter of the earcanal. 
     
     
       8. An earplug as defined in claim 1, wherein said second passage provides a horn effect. 
     
     
       9. An earplug as defined in claim 8, wherein each of said first and second passages is of uniform cross-sectional size, said second passage having a cross-sectional size greater than that of said first passage to obtain said horn effect. 
     
     
       10. An earplug as defined in claim 1, said acoustic resistance means comprising foraminous means positioned in proximity to said outer end of said first passage. 
     
     
       11. An earplug as defined in claim 1, further including acoustic compliance means in series relation to said first and second passages and operative to increase attenuation in a lower portion of the audible spectrum. 
     
     
       12. An earplug as defined in claim 11, said acoustic compliance means comprising a diaphragm positioned in proximity to the inner end of said second passage. 
     
     
       13. A protective earplug with improved audibility, comprising: an eartip assembly for insertion in an earcanal and constructed and arranged to produce an attenuation of audible sounds which increases with frequency within a major portion of an audible spectrum above approximately 50 Hz, and an external structure connected to said eartip to be positioned within an outer ear and defining a sound inlet for said earplug and a passage extending from said sound inlet to said eartip assembly, said passage being operative for enhancing response at audible frequencies above approximately 800 Hz to obtain a more uniform attenuation of sounds by the earplug over the aforesaid audible spectrum above approximately 50 Hz. 
     
     
       14. An earplug as defined in claim 13, wherein said eartip assembly comprises a generally cylindrical member of compressible foam material having a central opening therethrough and a tube having an inner end portion disposed in said opening, an outer end of said tube being coupled to an inner end of said passage of said external structure. 
     
     
       15. An earplug as defined in claim 14, a damping element disposed in proximity to the outer end of said tube and said inner end of said passage. 
     
     
       16. An earplug as defined in claim 14, a diaphragm element disposed in proximity to the outer end of said tube and said inner end of said passage and operative to increase attenution in a lower portion of the audible spectrum to obtain a still more uniform attenuation of sounds by the earplug over the audible spectrum. 
     
     
       17. A method of protecting the ear from damaging exposure to high intensity sounds while permitting recognition of sounds, comprising the steps of forming an eartip assembly for insertion in the ear including a central tube surrounded by compressible foam material, restricting passage of sound through said tube to dampen resonances which would otherwise be produced by an intrinsic mass acoustical reactance of said tube and an intrinsic compliance of the earcanal, and extending a passage from an outer end of the tube to a sound inlet to produce a resonant peak at a frequency at which intelligibility of sounds is enhanced and at which said passage has a length that is approximately equal to a quarter wavelength. 
     
     
       18. A method as defined in claim 17, including the additional step of adjusting the length of said passage according to requirements of a particular user or class of users. 
     
     
       19. An earplug as defined in claim 1, said first passage means comprising a sound tube in a custom earmold.